Display tube with color selective filtration

ABSTRACT

A cathode ray display tube having color selective filtration for providing improvement in viewability of a display by providing higher brightness for a given contrast ratio, this being achieved by providing within the resin material which bonds the implosion panel to the faceplate a filter in the form of a thin film having color characteristics matched to the color of the emission from the phosphor screen of the tube.

United States Patent Robinder Mar. 25, 1975 [54] DISPLAY TUBE WITH COLOR SELECTIVE 2,734,142 2/1956 Barnes 313/112 X FILTRATION 2,804,803 9/1957 Edwards et a1. 313/1 12 X v 3,209,191 9/1965 Hamilton 313/110 Inventor: Ronald Rvblnder, Marshfleld, 3,382,393 5/1968 Schwartz 313/112 x Mass. 3,638,060 1/1972 Wacher 313/112 [73] Assignee: Raytheon Company, Lexington,

Mass Primary Examiner-Alfred L. Brody Attorney, Agent, or Firm-Harold A. Murphy; Joseph [22] F1169: 1974 D. Pannone; John T. Meaney [21], Appl. No.: 454,186

[57] ABSTRACT U.S. 16, A cathode ray tube having olor Selective 3 13/466 tration for providing improvement in viewability of a [51] Cl. providing brightness for a given con Fleld Search 1 466; trast ratio, this being achieved by providing within the 78/7.85, 7.86; 358/71-73; 220/2.3 A resin material which bonds the implosion panel to the faceplate a filter in the form of a thin film having color 1 References Clted Characteristics matched to the color of the emission UNITED STATES PATENTS from the phosphor screen of the tube. 2,290,186 7/1942 Holman et al. 313/112 X 2,618,759 11/1952 Hoyt 313/112 x 5 6 Drawmg guns PATENTEU I975 sum 1 pr '3 PERCENT TRANSMISSION 3'00 460 560 660 NANOMETERS sum 2 or 3 a 60- 2 5 5o Z CC I- 40 2 LU 3O uJ CL on I Y I I r 700 300 400 500 600 700 NANOMETERS 360 4'00 sbo 660 7b0 NANOMETERS PATENTEUmzsms S ISSION NITS) EMISSION OR TRAN (ARBITRARY u SI'IU 3 [IF 3 NANOMETERS DISPLAY TUBE WITH COLOR SELECTIVE FILTRATION BACKGROUND OF THE INVENTION In the manufacture and use of a color television type display tube, problems very frequently occur when tubes exhibiting poor contrast are used in areas with high ambient illumination levels. Most known devices employ neutral density filtration in an attempt to achieve good viewability in high ambient illumination conditions. This is done by providing colloidal absorbers such as silver in'the glass composition of the tube faceplate or the implosion panel to produce a gray or black device. I

The approach of selective filtration has been used for various special products in the past. Such known approaches include the use of colored glass for either the tube faceplate or the implosion panel, which glass is difficult and expensive to obtain and cannot be readily tailored to possess the exact desired spectral properties. Another approach includes coloration of the bonding material between the faceplate and the implosion panel. This approach has been unsatisfactory since it resulted in undesirable shading due to the differences in thickness of the resin bonding material across the face of the tube.

SUMMARY OF THE INVENTION In accordance with the present invention, considerable improvement in viewability has been achieved by providing selective color filtration which provides higher brightness and a given contrast ratio. This is achieved by locating within the resinous bonding material between the faceplate and the implosion panel a thin film of a specific color which is selected to match the color of the light emitted from the phosphor screen within the tube. For example, such a film may comprise an organic filter substance such as dye in a gelatin or plastic film, which films are available in a wide variety of shades to give improved color matching with the phosphor emission. In such a structure the problem of shading is avoided since the filter film is made separately from the bonding layer and has a uniform thickness. It enables the production of a simple structure which can be readily sandwiched between the tube faceplate and the implosion panel when the panel is being assembled with the faceplate.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objectives of this invention will become apparent from the following description taken in connection with the accompanying drawings, wherein:

FIG. I is an elevational view in partial section of a cathode ray display tube embodying the invention.

FIG. 2 is an enlarged fragmentary sectional view of a portion of the front end structure of the tube as shown in FIG. 1.

FIGS. 3, 4 and 5 are graphs illustrating the light emitting characteristics of selected films utilizable with the present invention; and

FIG. 6 is a graph comparing P44 phosphor emission spectra with certain selected filters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A cathode ray tube of the display type is indicated at 10 in FIG. 1 and isutilized for providing a visual display which may be viewed in the normal manner of tubes of this type. It is well known that such display tubes are often required to be used under conditions when high ambient illumination levels are present. For example, in the cockpit of aircraft the ambient light often exists at such high illumination levels as to render observation of displays extremely difficult when conventional tube structures-are used.

In the present invention viewability of a display is considerably improved even under conditions of high ambient illumination levels. This is achieved by selective color filtering whereby ambient illumination is decreased while the emitted light from the tube is enhanced.

Referring particularly to FIGS. 1 and 2, the tube 10 embodies the usual evacuated envelope which includes a bulb portion 12 and a narrow neck portion 14 at one end thereof. At the other end of bulb portion 12 the envelope is closed by a faceplate 16 which is usually an integral part thereof. The faceplate 16 carries on its inner surface a layer 18 of electron-sensitive phosphor. The faceplate 16 is preferably of glass so that light from the phosphor layer 18 will be transmitted externally of the tube for viewing. The phosphor material in layer 18 may be any of the well-known materials which have been found suitable for the purpose and which comprise relatively closely packed crystals which become fluorescent when bombarded by electrons.

Within the neck portion 14 is positioned a cathode ray gun (not shown) which may be of any suitable construction and which is adapted to be supplied with operating potential through leads or pins 20 which extend through the end of the envelope. Operation of the cathode ray gun will cause the formation of an electron beam which can be made to scan the phosphor layer 18 in the normal manner of tubes of this character. This will cause the phosphor to become luminescent in the areas which are contacted by the scanning electron beam. The resultant light from the phosphor will travel outwardly of the envelope through the faceplate 16 externally of the tube for viewing by an observer.

It has become common practice to provide an implosion panel 22 adjacent the outer surface of the faceplate for safety purposes. Such an implosion panel may be separate from the tube structure but, in accordance with the present invention, is secured directly to the faceplate 16 by means of a layer 24 of suitable adhesive. The adhesive will be preferably a clear resin such as an epoxy sold by Dow Corning as Epoxy TV-720, for example.

In a normal tube structure of the character described above, it has been found that ambient light falling on the phosphor layer 18 after passing through the implosion panel 22, resin layer 24 and faceplate 16 will seriously interfere with the visability of the light image produced by phosphor layer 18. In accordance with the present invention, ambient light is considerably attenuated by means of a filter which is located preferably within the resin layer 24. This filter is conveniently provided in the form of a thin film 26 of gelatin or plastic which is provided with a color which substantially matches the color of the light emitted by the phosphor.

The film 26 may be, for example, about 0.0100.020 inches thick and the entire resin-film thickness may be about 0.1-0.2 inches thick, for example. The plastic material for the film 26 may be any suitable lighttransparent plastic such as vinyl acetate or butyrate. 1f gelatin is used for the film 26 it may be, for example. Wratten No. 99.

A particularly suitable example of gelatin films for use in the invention are the films made by Eastman Kodak Co. or Rosco Labs. which can be obtained by calling for their numbered types. Typically, Rosco Labs films 817 are suitable for use with P14 phosphor which emits light predominantly in the 600-700 nanometer range, thus being somewhat orange in color. This is indicated in FIG. 3 wherein the spectral transmission of the 817 film is shown as being predominant in the 600-700 nanometer range to provide the orange or dark amber transmission characteristics.

Rosco Labs. film No. 821 is shown in FIG. 4 as transmitting predominantly in the red region of the spectrum between about 640 and 700 nanometers. This film No. 821 is. therefore, suitable for use with P22 phosphor which emits in the red.

Rosco Labs. film No. 874 transmits predominantly between 500 and 540 nanometers and, therefore, is intended for use with P31 phosphor which emits green light.

In the following tables, the emitted radiation is for either P44 or P22 phosphor, and it is assumed that under given conditions of electron excitation the emission of P44 is about 200 ft-L and P22 is about 1 ft-L. Emitted radiation B is computed according to B 1,. T T, T

R 0.85 T; T, T 1,,

Contrast (CR) is defined as the ratio of emitted light plus reflected light to reflected light.

Tables A and B which follow are two examples of conventional devices utilizing neutral density filters.

TABLE A Emitted Light (P44) Reflected Light T, .11 .1 l T, 1.00 1.00 T; .55 .55

B=(200)(.1l)(.55) 12.1 ft-L R (5500)(.85)(.lll(.1 l )(.55)(.55) 17.0 ft-L TABLE B Emitted Light (P22) Reflected Light T .1 1 .1 1 T, 1.00 1.00 T. .55 .55

The following Tables are examples of different embodiments of the present invention.

TABLE C Eastman Kodak Co. No. 74 gelatin film T,

Emitted Light (P44) Reflected Light T, .9 .9 T, .1 .04 T. 9 .9

R=(550011.851091 0041 191 4. ft-L TABLE D Eastman Kodak Co. No. 99 gelatin film T, Emitted Light (P44) Reflected Light T, .9 .9 T, .19 .07 T 9 v9 B (20011910191191 30 ft-L R (5500)t.85)(.9) (.07) (.9) 15 ft-L 5 CR R 15 -3.0

TABLEE (Same as Table D except T, has neutral gray tint) Eastman Kodak Co. No. 99 gelatin Film T,

Emitted Light (P44) Reflected Light T, .55 .55 T, .19 .07 T" 9 .9

TABLE F Eastman Kodak Co. No. 29 gelatin film T,

From the foregoing it will be apparent that color selective filtration as described provides a definite improvement in contrast ratio and, therefore, in viewability ofa cathode ray tube display by giving higher brightness for a given contrast ratio. lt will be noted that the combination of the Eastman Kodak No. 99 film with either the 55% transmissive or the 90 percent transmissive glass layers as shown in Tables D and E gives better overall performance than film No. 74 (Table C) when used with P44 phosphor. This can be understood by reference to FIG. 6 from which it will be seen that the transmission spectrum of film No. 99 obviously represents a better spectral match with P44 phosphor than the No. 74 film.

Even better performance is obtained with a red phosphor and filter as shown in Table G. It has been found that still better results are achieved by using a blue phosphor and filter although in some applications where blue sky ambient illumination, for example, occurs this may slightly reduce the effective contrast.

This invention can be made by conventional and known tube manufacturing techniques wherein the tube envelope and components are first assembled, evacuated and tested. Following this the implosion panel 22 is. placed in overlying relation with the faceplate 16, with suitable spacers therebetween to regulate the size of the space to be filled with adhesive resin. At

this time the film 26 is also located between the faceplate and panel and similarly spaced from these elements. A securing tape is mounted around the circumference of the two members and after the spacers are removed the tape holds the members in the predetermined spaced relation. Heat of about 60C is applied and the spaces on both sides of the film are filled with resin, after which the final assembly is cooled and the resin is allowed to set. i

From the foregoing it will be apparent that all of the objectives of this invention have been achieved by the structures shown and described. It will be apparent. however, that various modifications of this invention may be made by those skilled in the art without departing from the spirit of the invention as expressed in the accompanying claims. Therefore, all matter shown and described is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. A display tube comprising an evacuated envelope having a transparent faceplate in one wall thereof, a light-generating layer disposed adjacent the inner side of said faceplate, and adapted to emit light of a predetermined color, a transparent protective panel adjacent the outer side of the faceplate and spaced therefrom, a layer of transparent bonding material in said space between the faceplate and panel, and a light-filtering film disposed within said bonding material and having a selected color which approximates the color of the light emitted by said light-generating layer.

2. A display tube as set forth in claim 1 wherein said bonding material is a resin, and said film is a plastic.

3. A display tube as set forth in claim 1 wherein said light-generating layer emits light predominately between about 600-700 nanometers in wavelength and said film absorbs light of substantially all other wavelengths.

4. A display tube as set forth in claim 1 wherein said light-generating layer emits light predominately between about 475575 nanometers in wavelength, and said film absorbs light of substantially all other wavelengths.

5. A display tube comprising an evacuated envelope having a transparent faceplate at one end thereof, a layer of light-generating phosphor on the inner surface of said faceplate, electron beam-producing means in the opposite end of the envelope, said phosphor being responsive to impingement by electrons from said means to generate light of a predetermined color, a transparent protective panel adjacent the outer side of the faceplate and spaced therefrom, a layer of transparent bonding material in said space between the faceplate and panel, and a light-filtering film disposed within said bonding material and having a selected color which approximates the color of the light emitted by said light-generating layer. 

1. A display tube comprising an evacuated envelope having a transparent faceplate in one wall thereof, a light-generating layer disposed adjacent the inner side of said faceplate, and adapted to emit light of a predetermined color, a transparent protective panel adjacent the outer side of the faceplate and spaced therefrom, a layer of transparent bonding material in said space between the faceplate and panel, and a light-filtering film disposed within said bonding material and having a selected color which approximates the color of the light emitted by said lightgenerating layer.
 2. A display tube as set forth in claim 1 wherein said bonding material is a resin, and said film is a plastic.
 3. A display tube as set forth in claim 1 wherein said light-generating layer emits light predominately between about 600-700 nanometers in wavelength and said film absorbs light of substantially all other wavelengths.
 4. A display tube as set forth in claim 1 wherein said light-generating layer emits light predominately between about 475-575 nanometers in wavelength, and said film absorbs light of substantially all other wavelengths.
 5. A display tube comprising an evacuated envelope having a transparent faceplate at one end thereof, a layer of light-generating phosphor on the inner surface of said faceplate, electron beam-producing means in the opposite end of the envelope, said phosphor being responsive to impingement by electrons from said means to generate light of a predetermined color, a transparent protective panel adjacent the outer side of the faceplate and spaced therefrom, a layer of transparent bonding material in said space between the faceplate and panel, and a light-filtering film disposed within said bonding material and having a selected color which approximates the color of the light emitted by said light-generating layer. 